Stent with enhanced friction

ABSTRACT

A stent for placement in a body lumen is fabricated by forming a tube having an un-deployed diameter sized for the tube to be placed on a deployment balloon and advanced through a body lumen to a deployment site. The tube is expandable upon inflation of the balloon to an enlarged diameter sized for the tube to be retained within the lumen at the site upon deflation and withdrawal of the balloon. The tube has a stent axis extending between first and second axial ends of the tube. The tube has an exterior surface and an interior surface. The tube is polished to polish the exterior surface to a smooth surface finish and with at least a portion of the interior surface having a rough surface finish rougher than the surface finish of the exterior surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to stents for use in intraluminal applications.More particularly, this invention pertains to a stent with enhancedfriction on a delivery catheter.

2. Description of the Prior Art

Stents are widely used for numerous applications where the stent isplaced in the lumen of a patient and expanded. Such stents may be usedin coronary or other vasculature, as well as other body lumens.

Commonly, stents are cylindrical members. The stents expand from reduceddiameters to enlarged diameters. Frequently, such stents are placed on aballoon catheter with the stent in the reduced-diameter state. Soplaced, the stent is advanced on the catheter to a placement site. Atthe site, the balloon is inflated to expand the stent to the enlargeddiameter. The balloon is deflated and removed, leaving the enlargeddiameter stent in place. So used, such stents are used to expandoccluded sites within a patient's vasculature or other lumen.

Examples of prior art stents are numerous. For example, U.S. Pat. No.5,449,373 to Pinchasik et al. teaches a stent with at least two rigidsegments joined by a flexible connector. U.S. Pat. No. 5,695,516 toFischell teaches a stent with a cell having a butterfly shape when thestent is in a reduced-diameter state. Upon expansion of the stent, thecell assumes a hexagonal shape.

To deliver a stent, the stent in a reduced diameter shape is placedsurrounding a deflated tip of a balloon catheter. The catheter and stentare simultaneously advanced through a sheath to a deployment site in abody lumen. At the site, the balloon is inflated to expand the stent.Following such expansion, the balloon is deflated. The catheter iswithdrawn leaving the expanded stent in place.

In order to prevent the presence of sharp comers and burrs which mightotherwise damage a balloon, stents are highly polished to a mirrorfinish. Unfortunately, a highly polished stent can slip off a balloontip catheter. Also, when a balloon is inflated, the axially spaced endsof the balloon tend to inflate faster than the center of the balloon.This can result in a concave cross-section (when viewed from the side)in the balloon and stent at a point in time prior to full expansion ofthe stent. During this period, ends of the stent may slide toward oneanother on the balloon toward the center of the balloon resulting in anundesirable compression of the length of the stent.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a stentfor placement in a body lumen is fabricated by forming a tube having anun-deployed diameter sized for the tube to be placed on a deploymentballoon and advanced through a body lumen to a deployment site. The tubeis expandable upon inflation of the balloon to an enlarged diametersized for the tube to be retained within the lumen at the site upondeflation and withdrawal of the balloon. The tube has a stent axisextending between first and second axial ends of the tube. The tube hasan exterior surface and an interior surface. The tube is polished topolish the exterior surface to a smooth surface finish and with at leasta portion of the interior surface having a rough surface finish rougherthan the surface finish of the exterior surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of a stent;

FIG. 2 is the view of FIG. 1 with a nozzle poised to spray a particulatematter against the interior of the stent according to the presentinvention;

FIG. 3 is a cross-sectional view of a rib of the stent of FIG. 1 beforetreatment according to the present invention; and

FIG. 4 is the view of FIG. 3 following treatment according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the several drawing figures in which identical elementsare numbered identically, a description of the preferred embodiment ofthe present invention will now be provided. Where several embodimentsare shown, common elements are similarly numbered and not separatelydescribed with the addition of apostrophes to distinguish theembodiments.

In FIG. 1, a stent 10 is shown. The stent 10 is a hollow reticulatedtube having an axis X—X and extending between first and second ends 12,14. The stent 10 is shown in a reduced diameter state sized to beadvanced through a human body lumen to a deployment site in the lumen.By way of non-limiting representative example, the stent may have anaxial length L of about 9 mm-76 mm depending on the intended use of thestent (e.g., for opening an occluded site in a coronary artery or otherbody lumen). By way of none limiting representative example, such astent 10 may have a reduced or unexpanded diameter D of 2.0 mm and beexpandable to an expanded diameter of 10 mm.

For purposes of illustration, the present invention is described withreference to a stent 10 having a structure such as more fully describedin commonly assigned and copending U.S. patent application Ser. Nos.09/049,486 filed Mar. 27, 1998, now U.S. Pat. No. 6,132,460, and09/069,347 filed Apr. 29, 1998, now U.S. Pat. No. 6,132,461. Such astent 10 is formed from a hollow, solid wall tube of stent material(e.g., titanium, Nitinol, stainless steel etc.). Excess material of thetube is removed through any suitable means such as laser cutting orchemical etching. Removal of the excess material leaves a stent 10having a plurality of ribs 16 defining a plurality of open cells 18extending through the wall thickness of the stent 10. The ribs 16 haveinterior surfaces 16 a (FIGS. 3 and 4) facing the axis X—X and exteriorsurfaces 16 b facing away from the axis X—X. The interior and exteriorsurfaces 16 a, 16 b are joined by radial surfaces 16 c.

In use, the reduced diameter stent 10 is placed on a balloon-tippedcatheter. During such placement, the catheter balloon is deflated andthe stent 10 is surrounding the balloon. The catheter and mounted stentare passed through the patient's lumen. Commonly, the catheter and stentare advanced through a catheter sheath pre-positioned within the lumen.The catheter and stent are advanced through an open distal end of thesheath to the deployment site within the lumen. At this point, theballoon is inflated to expand the stent 10 to the expanded diameter.After such expansion, the balloon is deflated and the catheter iswithdrawn leaving the expanded stent 10 positioned within the lumen.

It will be appreciated that the foregoing description of stent 10 andits placement using a balloon-tipped catheter are previously known. Suchdescription is provided to clarify the benefits of the presentinvention.

When forming a stent 10 from a solid wall tube as described, surfaceimperfections may be formed on the stent 10. For example, these caninclude sharp edges between surfaces 16 a and 16 c or surfaces 16 b and16 c. Further, such imperfections may include burrs. Such imperfectionsare undesirable. A sharp surface imperfection at the interior surface 16a can damage a catheter balloon thereby degrading or precluding itsdesired performance. A surface imperfection on the exterior surface 16 bcan cause the stent 10 to be difficult to advance through a cathetersheath to the desired deployment site.

Recognizing the undesirability of such surface imperfections, the priorart uses polishing techniques to polish a stent 10 to a high degree ofsmooth surface finish for all of surfaces 16 a, 16 b and 16 c.Unfortunately, such a highly polished stent 10 presents additionalproblems. Namely, the exterior surfaces of catheter balloons areslippery relative to the material of a highly polished stent 10.Therefore, a stent 10 can be displaced on or fall off a catheterballoon. Also, when a balloon is inflated, the axially spaced ends ofthe balloon tend to inflate faster than the center of the balloon. Thiscan result in a concave cross-section (when viewed from the side) in theballoon. Since the highly polished stent 10 is slidable on the balloon,the ends 12, 14 of the stent 10 may tend to slide toward one anotherwhen the balloon is in the intermediate concave state. Such movement canresult in an undesirable compression of the length L of a highlypolished stent 10.

The prior art has suggested the use of so-called “sticky” balloon whichare coated or otherwise formed with a material having an enhancedadhesion with a highly polished inner surface 16 a of a stent 10.However, such balloons are difficult and expensive to manufacture.

The present invention selective roughens the interior surface 16 a ofthe stent 10 to enhance friction between the stent 10 and a catheterballoon. Such a roughening is counter-intuitive since conventional stentconstruction theory calls for a smooth, highly polished stent to avoidor minimize raised areas which might otherwise provide sites forthrombus formation or platelet activation after the stent is deployed.However, test data have indicated that a stent 10 with roughenedsurfaces as will be described does not exhibit excessive thrombusformation or platelet activation.

The interior surface 16 a of the stent 10 is roughened to a roughsurface finish rougher than the surface finish of the exterior surface16 b. In the roughening process as will be described, the radialsurfaces 16 c are also roughened.

In a preferred embodiment, only a limited area between ends 12, 14 ofthe interior surface 16 a is roughened. This area is shown in FIG. 1 asbounded between lines 12 a, 14 a spaced about 4 mm into the interior ofthe stent 10 from ends 12, 14. The roughened area completely surroundsthe axis X—X. While the entire interior surface 16 a could be roughened,it is preferred that at least areas on opposite sides of a center-lineCL of the stent 10 be roughened to prevent axial shortening of thestent. Preferably, the boundaries 12 a, 14 a of the roughened area areas close as possible to ends 12, 14 to prevent even a small amount ofaxial shortening.

As shown in FIG. 2, the roughening is provided by a nozzle 30 positionedadjacent an end (e.g., end 12) of the stent 10. The nozzle 30 ispositioned with a nozzle orifice 32 directing a particulate stream at anangle relative to the stent axis X—X. In a preferred embodiment, theorifice is positioned 1.0 mm from end 12 and the angle is 30°. By way ofexample, the nozzle 30 is a product sold under the name “Microblaster”of Comco, Inc. and has an orifice diameter of 0.015 inch. Theparticulate stream is powder silicon carbide size of about 50 micronwhich is discharged from the orifice at a pressure of 60 psi. During theapplication of the particulate stream, the stent 10 is rotated 360°about its axis X-X. When it is desirable to limit the axial length ofthe roughened area, a rod (not shown) may be inserted through theopposite end 14 of the stent 10 to expose only the area 12 to beroughened. Following roughening through end 12, the procedure isrepeated on the opposite end 14 to uniformly roughen the surface 16 a.If desired, a tube may be placed around the exterior surface 16 b toinsure the exterior surface 16 b is not roughened by the process. In theroughening process, the radial surfaces 16 c are also roughened.Roughening of the radial surfaces 16 c is not essential to the presentinvention. However, such roughening is not detrimental.

The surfaces 16 a, 16 c are uniformly covered with pits which areapproximately 3 to 20 microns in size.

With a stent 10 as described, the stent 10 has enhanced friction on adeployment balloon. Slippage of the stent 10 on the balloon is reducedand integrity of the axial length L of the stent 10 is maintained. Also,and surprisingly, the stent 10 performs without undue thrombus formationor platelet activation in the roughened area of surface 16 b.

From the foregoing, the present invention has been shown in a preferredembodiment. Modifications and equivalents are intended to be includedwithin the scope of the appended claims.

What is claimed is:
 1. An intraluminal stent comprising: a tube havingan un-deployed diameter sized for the tube to be placed on a deploymentballoon and advanced through a body lumen to a deployment site; saidtube expandable upon inflation of said balloon to an enlarged diametersized for said tube in said enlarged diameter to be retained within saidlumen at said site upon deflation and withdrawal of said balloon; saidtube having a stent axis extending between first and second axial endsof said tube; said tube having an exterior surface and an interiorsurface; said interior surface including at least a portion having arough surface finish rougher than a surface finish of said exteriorsurface.
 2. A stent according to claim 1 wherein said portion includesfirst and second portion of said rough surface finish disposed onopposite sides of a center of said tube.
 3. A stent according to claim 2wherein said portion extends along substantially an entire axial lengthof said tube.
 4. A method for fabricating a stent for placement in abody lumen, said method comprising: forming a tube having an un-deployeddiameter sized for the tube to be placed on a deployment balloon andadvanced through a body lumen to a deployment site, said tube expandableupon inflation of said balloon to an enlarged diameter sized for saidtube in said enlarged diameter to be retained within said lumen at saidsite upon deflation and withdrawal of said balloon, said tube having astent axis extending between first and second axial ends of said tube,said tube having an exterior surface and an interior surface; polishingsaid tube to polish said exterior surface to a smooth surface finish andwith at least a portion of said interior surface having a rough surfacefinish rougher than said exterior surface finish.
 5. A method accordingto claim 4 wherein both said exterior surface and interior surface arepolished to remove balloon threatening burrs and said portion of saidinterior surface is subsequently roughened to said rough surface finish.6. A method according to claim 5 wherein said rough surface finish isapplied at least on opposite sides of a center of said tube.
 7. A methodaccording to claim 6 wherein said rough surface finish is appliedsubstantially entirely along an axial length of said interior surface.